High purity hydrogen can be produced by the water-gas shift reaction of carbon monoxide in the presence of steam. The equation for this reaction is: EQU CO+H.sub.2 O.LAMBDA.H.sub.2 +CO.sub.2
High purity hydrogen is conventionally recovered from the product gas by hydrogen PSA using a carbon dioxide-selective adsorbent. Often, the carbon monoxide that is used as feed for the shift reaction is produced by reforming or partially oxidizing hydrocarbon-containing substances, such as natural gas. The product gas from these reactions contains hydrogen, carbon monoxide and carbon dioxide.
A major disadvantage of producing high purity hydrogen by the water-gas shift reaction using the above-mentioned feedstocks occurs in the hydrogen recovery stage, i.e. the hydrogen PSA step. The yield and purity of hydrogen recovered from gas mixtures by PSA is somewhat dependent upon the concentration of impurities in the feed gas to the PSA system. The efficiency of the hydrogen recovery drops as the concentration of impurities such as carbon monoxide and carbon dioxide in the PSA feed gas increases.
The above-described hydrogen PSA process can be improved by removing carbon dioxide from the feedstock to the water-gas shift reactor. This can be accomplished, for example, by means of membrane separation or PSA. However, removal of carbon dioxide from the feedstock to the water-gas shift reaction adds considerable cost to the high purity hydrogen production process, and may make the modified process economically unfeasible.
It is often desirable to produce high purity carbon monoxide for use in various chemical processes. The shift reaction feedstocks discussed above are excellent sources of carbon monoxide. However, the above-described process does not provide for the efficient production of high purity carbon monoxide.
It would be desirable to enhance the yield and purity of the hydrogen PSA process, and to provide for the coproduction of high purity carbon monoxide. This invention accomplishes these objectives.